The 86-year-old liberal philanthropist said that Brexit negotiations should be held in a "constructive spirit" and at the same time the EU should make itself attractive again to people, especially younger generations.

Soros, who became known as the man who broke the Bank of England after making £1bn of winning bets against sterling in the 1992, also warned Brussels that talks with Britain will take more than twice the two years both sides have allowed.

He wrote: "Negotiating the separation with Britain will divert the EU's attention from its own existential crisis, and the talks are bound to last longer than the two years allotted to them. Five years seems more likely."

Soros warned that the single currency area had become "the exact opposite of what was originally intended".

He wrote: "The European Union was meant to be a voluntary association of like-minded states that were willing to surrender part of their sovereignty for the common good.

Refugee crisis

"After the financial crisis of 2008, the eurozone was transformed into a creditor/debtor relationship where the debtor countries couldn't meet their obligations and the creditor countries dictated the terms that the debtors had to meet.

"By imposing an austerity policy they made it practically impossible for the debtor countries to grow out of their debts. The net result was neither voluntary nor equal.

"Instead of a 'multi-speed' Europe we should aim for a 'multi-track' Europe that would allow member states a wider variety of choices. This would have a far-reaching beneficial effect."

He urged the bloc to focus on three key areas – dealing with the refugee crisis, Brexit and "the lack of an economic growth strategy".

George Soros also accused the Hungarian prime minister Viktor Orbán of building a "mafia state", as he warned the fate of the Central European University (CEU) he founded hangs in the balance.

The financier was confident the university's defence of itself would ultimately "bring the slow-moving wheels of justice into motion", but said it and other organisations he had backed were still at risk under the Orbán-led government.

Hungary's populist prime minister has introduced tough measures for the registration of foreign-registered universities that could force the closure of the CEU, one of the top academies in the region. Thousands of people protested in Budapest in April against a bill seen by many as targeting the university.